The invention generally relates to a layered design for a fuel cell flow field plate.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, hydrogen (a fuel) is reacted to produce protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the protons to form water. The anodic and cathodic reactions are described by the following equations:H2→2H++2e− at the anode of the cell, andO2+4H++4e−→2H2O at the cathode of the cell.
A typical fuel cell has a terminal voltage of up to about one volt DC. For purposes of producing much larger voltages, multiple fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow field plates (graphite composite or metal plates, as examples) that are stacked one on top of the other. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. A PEM is sandwiched between each anode and cathode flow field plate. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to act as a gas diffusion media and in some cases to provide a support for the fuel cell catalysts. In this manner, reactant gases from each side of the PEM may pass along the flow channels and diffuse through the GDLs to reach the PEM. The PEM and its adjacent pair of catalyst layers are often referred to as a membrane electrode assembly (MEA). An MEA sandwiched by adjacent GDL layers is often referred to as a membrane electrode unit (MEU).
Referring to FIG. 1, as an example, a fuel cell stack 10 may be formed out of repeating units called plate modules 12. In this manner, each plate module 12 includes a set of composite plates that may form several fuel cells. For example, for the arrangement depicted in FIG. 1, an exemplary plate module 12a may be formed from a cathode cooler plate 14, a bi-polar plate 16, a cathode cooler plate 20, an anode cooler plate 18, a bipolar plate 22 and an anode cooler plate 24 that are stacked from bottom to top in the listed order. The cooler plate functions as a heat exchanger by routing a coolant through flow channels in either the upper or lower surface of the cooler plate to remove heat from the plate module 12a. The surface of the cooler plate that is not used to route the coolant includes flow channels to route either hydrogen (for the anode cooler plates 18 and 24) or oxygen (for the cathode cooler plates 14 and 20) to an associated fuel cell. The bipolar plates 16 and 22 include flow channels on one surface (i.e., on the top or bottom surface) to route hydrogen to an associated fuel cell and flow channels on the opposing surface to route oxygen to another associated fuel cell. Due to this arrangement, each fuel cell may be formed in part from one bipolar plate and one cooler plate, as an example.
For example, one fuel cell of the plate module 12a may include an MEU located between the anode cooler plate 24 and the bipolar plate 22. In this manner, the upper surface of the bipolar plate 22 includes flow channels to route oxygen near the cathode of the MEU, and the lower surface of the anode cooler plate 24 includes flow channels to route hydrogen near the anode of the MEU.
As another example, another fuel cell of the plate module 12a may be formed from another MEU that is located between the bipolar plate 22 and the cathode cooler plate 20. In this manner, the lower surface of the bipolar plate 22 includes flow channels to route hydrogen near the anode of the MEU, and the upper surface of the cathode cooler plate 20 includes flow channels to route oxygen near the cathode of the MEU. The other fuel cells of the plate module 12a may be formed in a similar manner.
FIG. 2 depicts a surface 100 of a prior art anode cooler flow field plate 90 (conducting fuel on one side and coolant on the other). The surface 100 includes flow channels 102 for communicating a coolant to remove heat from the fuel cell stack 10. Coolant enters channels 102 via manifold opening 166, and exits channels 102 via manifold opening 162.
FIG. 3 depicts an opposite surface 119 of the anode cooler plate 90 used for communicating hydrogen (for an anode cooler plate configuration) or air (for a cathode cooler plate configuration) to a fuel cell MEU positioned between two plates. As an example, an opening 170 of the plate 90 forms part of a manifold for introducing hydrogen to the flow channels 120 (see FIG. 3); and an opening 168 of the plate 90 forms part of a manifold for removing hydrogen from the flow channels 120. Likewise, openings 190 and 164 form part of the inlet and outlet manifolds used to introduce and remove air from the flow channels on the cathode side of a flow field plate (not shown).
Conventionally, each flow field plate includes a gasket groove on its upper surface to receive a gasket 190. Thus, the gasket groove defines the “up side” of the flow field plate. However, the gasket 190 may be adhered to either side of the anode cooler plate 90, and thus, some anode cooler plate designs may not include a gasket groove. To form a fuel cell, an MEU is generally sandwiched between the reactant flow fields of 2 such plates.
There is a continuing need for fuel cell designs adapted to achieve objectives including the foregoing in a robust, compact, and cost-effective manner.